To sterilize many foods, pharmaceuticals and other products, to make them “shelf-stable,” the products are subjected to a sterilization method by heating the food in its sealed container to a predetermined temperature. The product is held at this temperature for a product specific duration. This process is commonly referred to as an autoclave process, retort process or a sterilization process.
A retort is a pressure vessel commonly used in the food industry for pasteurization and sterilizing low acid food in the container.
Water spray retorting is one of several acceptable commercial processes available in the food industry suitable to run process designed for pasteurizing and sterilizing containers requiring overpressure to ensure integrity of the container. In a water spray process, water is traditionally circulated via a pump circulation loop that draws the water from a sump in the bottom of the retort and pumps the water through a distribution header fitted with spray nozzles at the top and or sides of the retort. The distribution pipes run along the length of the vessel. Steam is used for heating the product in the retort using distribution pipes located in the sump to heat the recirculated water as well as distribution pipes above the sump to distribute saturated steam directly into the load. Compressed air is used to develop overpressure in the retort throughout the process to offset the pressure differential inside the container. Each distribution header has a defined number of spray nozzles that distribute water throughout the product load. There are typically 5-7 headers positioned around the product load. Each nozzle has a given flow and spray angle required to assist with a desired homogeneous heat transfer.
Water cascade retorting is another acceptable commercial processes available in the food industry suitable to run process designed for pasteurizing and sterilizing containers requiring overpressure to ensure integrity of the container. In a water cascade process, water is traditionally circulated via a pump circulation loop that draws the water from a sump in the bottom of the retort and pumps the water through a distribution header oriented at the top and or sides of the retort. The distribution pipes run along the length of the vessel. The header includes openings which allow water to flow down into the into a metal pan that runs the length of the retort above the product. The metal pan typically fills with water to a depth of about 12 mm to 20 mm, and has openings allowing the water to trickle or cascade from the pan (under the head pressure of the water depth in the pan), down to and through the product from the top down through the load. The openings are typically sized and spaced to define such that only between about 3% and about 6% of the pan surface is open. A typical diameter of the openings may be on the order of about 6 mm to 9 mm, with a density distribution to result in a center to center spacing between the openings of about 40 mm. The water is heated in the sump by direct steam or through a heat exchanger in the circulation loop.
For the purpose of treating stationary paperboard containers, U.S. Pat. No. 7,104,465 discloses a water spray retort vessel with at least one processing station and a processing method that includes spraying process fluid onto a container having a paperboard component at a given total flow rate and pressure, where the processing fluid is sprayed onto the paperboard and working at a flow rate and pressure calculated to have a minimal droplet impact on the containers using one or more nozzles producing a solid cone spray pattern at a spray angle in the range of about 100 to about 115 degrees. The '465 patent also discloses that solid cone spray nozzles with higher angles can be used. However, the '465 patent fails to disclose how to calculate droplet impact for almost all spray distances. Moreover, the '465 patent fails to recognize that spraying a container with a minimal droplet impact does not leave room for fluctuations in water pressure during the retort process. Specifically, if the retort is designed to spray at a flow rate and pressure calculated to have a minimal droplet impact on containers while successfully heat treating, then any temporary drop in flow rate or pressure during the process could adversely affect the treatment operation. In other words, by focusing on minimal droplet impact, the '465 patent does not provide an adequately sized processing window for heat treatment of food products.
Modifying the spraying operation to spray with a higher droplet impact can overcome this problem with the '465 patent. However, such a modification can also exacerbate the problem that the '465 patent sought to solve, namely fluid absorption along the exposed edges of paperboard package containers. If there is too much absorption during the treatment process, the package will be considered defective.
Accordingly, what is needed is a system and method that provides an adequate processing window while at the same time avoiding adverse effects on paperboard packaging containers. This goal can be achieved by use of system in which water sprays are disrupted before they ever reach the packaged products being treated.